There are three classes of Fc gamma receptor proteins, Fc gamma RI (CD64), Fc gamma RII (CDw32), and Fc gamma RIII (CD16), which are encoded by at least eight genes. In this review we summarize some of the biological advances in the Fc gamma receptors during the past year, specifically: 1) identification of genes and their products; 2) regulation of gene expression and modulation of receptor number; 3) cellular functions and mechanisms of signal transduction; 4) ligand binding and the role of polymorphisms; and 5) soluble Fc gamma receptors. We also highlight the direct clinical applications of this Fc gamma receptor research.